An array antenna is a structure that utilizes a number of individual antenna elements held in fixed relation to one another to collectively generate one or more antenna beams. A phased array antenna is an array antenna that is able to steer a generated beam by varying an excitation phase associated with each of the antenna elements. A number of different factors dictate the overall antenna pattern that is generated by an array antenna. These factors include: the number of elements in the array, the type of elements in the array, the configuration of the elements, the signal amplitude applied to each element, and the excitation phase of each element. Design of an array antenna generally starts with a determination of the particular antenna pattern that is required by the underlying system. Once the pattern is known, the array is designed by appropriately choosing the above factors. Methods for performing such a design are well known in the art.
A problem arises in an array antenna when an element failure occurs. That is, when one or more of the antenna elements (or associated transmit/receive circuitry) become inoperative during system operation, the resulting antenna pattern will change due to changes in the above listed factors. For example, the modified antenna pattern may display decreased directivity/gain, increased sidelobe levels, or reduced range. Thus, the underlying antenna may no longer be capable of performing the function(s) it was designed to perform.
In the past, one method used to overcome a potential decrease in antenna performance due to element failure was to use an increased number of antenna elements in the antenna to achieve performance characteristics that exceed those necessary for the underlying system. Thus, as elements begin to fail, the antenna performance slowly degrades toward the level of performance required by the underlying system. This technique works well, but it consumes a greater amount of power than is necessary to perform the underlying antenna application. As can be appreciated, this inefficiency is generally undesirable, especially in applications where power is scarce, such as satellite communications.
Therefore, there is a need for a method and apparatus for efficiently maintaining a desired level of antenna performance in an array antenna should element failures occur.